Parameter control system for an oven

ABSTRACT

A parameter control system for an oven which may, for example, be a baking oven or a convection oven having the capability of injecting steam into the cooking cavity. The parameter control system precisely controls cooking temperature, cooking time, humidity and air flow in the oven. The parameters can be easily and repeatably set.

This invention relates to a parameter control system for an oven, forexample, a baking oven or, for example, a convection oven that also hasthe capability of injecting steam into the cooking cavity. Suchconvection ovens with steam-injection capability are known ascombi-ovens. Baking ovens or combi-ovens can be useful in a commercialkitchen for baking, steaming, proofing (or leavening), roasting, orholding products at a serving temperature. All combinations of heat andsteam are typically controlled by manual controls on the combi-oven.Baking ovens or combi-ovens may, for example, be deck ovens, tunnelovens, ferris-wheel ovens, carousel ovens or spiral ovens.

However, controls on these combi-ovens do not lend themselves to a "fastfood" or chain store use where precise control of cooking temperature,cooking time, humidity, and air flow must be easily set. Also theproduct quality must be repeatable for each store in the store chain.

U.S. Pat. No. 4,506,598-Meister relates to a combi-oven which has a hotair mode and also has a steam mode. A single fan circulates air duringboth modes. During the hot air mode a vent is open for the discharge ofvapor from the oven. During the steam mode, the vent is closed and whenthe steam displaces air out of the cooking chamber, the steam emergesout of the cooking space through a connection conduit. A control isactuated in accordance with a program during the hot air mode to controlthe position of a discharge pipe and a juice outflow pipe.

It is an object of the present invention, therefore, to provide a newand improved parameter control system for an oven for heating a foodproduct.

It is another object of the invention to provide a new and improvedparameter control system for a combi-oven for precisely controllingcooking temperature, cooking time, humidity and air flow in the oven.

It is another object of the invention to provide a new and improvedparameter control system for an oven in which the parameters can beeasily and repeatably set.

In accordance with the invention, a parameter control system for an ovenfor heating a food product comprises means for heating a heating mediumin the oven and programmed means for controlling as a first parameterthe temperature of the heating medium. The control system also includesprogrammed means for controlling as a second parameter the volumetricflow rate of the heating medium and programmed means for controlling oneor more time intervals for predetermined values of the temperature andvolumetric flow rate of the heating medium in the oven.

Also in accordance with the invention a heating system for an ovencomprises a plurality of product selection keys which upon one actuationof a first key selects at least one heating parameter for a givenproduct and which upon another actuation of the first key indicates anoven location for the given product.

Also in accordance with the invention, a parameter control system for anoven for heating a food product comprises means for heating medium inthe oven and programmed means for controlling as a first parameter thetemperature of the heating medium. The system also includes programmedmeans for controlling as a second parameter the humidity of the heatingmedium and programmed means for controlling one or more time intervalsfor predetermined values of the temperature and humidity of the heatingmedium..

Also in accordance with the invention, a parameter control system for anoven for heating a food product comprises means for heating a heatingmedium in the oven and programmed means for controlling as a firstparameter the temperature of the heating medium. The system alsoincludes programmed means for controlling as a second parameter thecirculation of the heating medium and programmed means for controllingone or more time intervals for predetermined values of the temperatureand circulation of the heating medium.

Also in accordance with the invention, a parameter control system for anoven for heating a food product comprises means for heating a heatingmedium in the oven and means for controlling a first parameter of aheating medium. The system also includes means for controlling one ormore time intervals for a predetermined value of the first parameter inwhich any of the time intervals is dependent on the measured value ofthe first parameter.

For a better understanding of the present invention together with otherand further objects thereof, reference is made to the followingdescription, taken in connection with accompanying drawings, and itsscope will be pointed out in the appended claims.

Referring now to the drawings:

FIG. 1 is a schematic diagram representing a parameter control system inaccordance with the invention;

FIGS. 2-5, inclusive, are flow charts comprising schematicrepresentations of a portions of a microcomputer which operatesaccording to computer programs produced according to the flow charts.

FIG. 6 is a graph representing a selected temperature difference vs.elapsed time characteristic of the cooking apparatus;

FIG. 7 is a flow chart comprising a schematic representation of aportion of a microcomputer which operates according to a computerprogram produced according to the flow chart.

FIG. 8 is a schematic diagram of an example of a closed-loop humiditycontrol apparatus;

FIG. 9 is a schematic diagram of an example of closed loop volumetricflow control apparatus; and

FIG. 10 is a schematic diagram of another example of closed loopvolumetric flow control apparatus.

Before referring to the drawings in detail, it will be understood thatfor purposes of clarity, the apparatus represented in block diagrams ofFIGS. 2-5 and 7 utilize, for example, an analog-to-digital converter anda microprocessor which includes such hardware as a central processingunit, program and random access memories, timing and control circuitry,input-output interface devices and other digital subsystems necessary tothe operation of a central processing unit as is well understood bythose skilled in the art. The microprocessor operates according to thecorresponding computer program produced according to the correspondingflow chart represented in the drawings.

Referring now more particularly to FIG. 1 of the drawings, amicrocomputer 10 includes a central processing unit which receives aninput from a keyboard 11 which may, for example, comprise a capacitivekeyboard.

The apparatus includes a conventional power supply 12, a reset circuit13 for resetting the microcomputer when renewing power in the powersupply, a clock oscillator 14 for providing clock pulses to themicrocomputer 10, a temperature sensor circuit 15 for sensing thetemperature when in the cooking apparatus, an audible alarm 16, analpha/numeric display 17 and indicator lights 18. The apparatus alsoincludes an input status circuit 19 which may, for example, beresponsive to a door switch (not shown). The microcomputer controlsoutput relay circuits 20 which may, for example, control electric orother heating means 20 of the oven.

Referring now more particularly to FIG. 2 of the drawings. When thestart key 30 is actuated, the program parameter variables per productkey, for example, time interval t₁, t₂, . . . t_(n), temperature T₁, T₂.. . T_(n), humidity H₁, H₂, . . . H_(n), volumetric flow rate V₁, V₂, .. . V_(n) and flow circulation R₁, R₂, . . . R_(n), are determined. Itwill be understood that where t_(n) represents a time interval, T_(n)equals the temperature setting for the time interval t_(n), H_(n) equalsthe humidity setting for the time interval t_(n), V_(n) equals thevolumetric flow rate for time interval t_(n), R_(n) equals the directionof flow circulation (left or right) for the time interval t_(n) and nequals 1, 2, 3 . . . n to the number of intervals. When a first productkey is pressed, a "product key pressed" microprocessor portion 32 iscoupled to a "load all initial (n=1) variables for product key intosetpoint registers" microprocessor portion 33.

The microprocessor portion 33 is coupled to an "enable temperature,humidity, volumetric and flow circulation algorithms" microprocessorportion 34.

The microprocessor portion 34 is coupled to a "prompt operator to selectshelf or batch and change product key function from product to shelf orbatch" microprocessor portion 35. The microprocessor portion 35 iscoupled to an "are measured parameters in oven within acceptable bandlimits" microprocessor portion 36. The "no" output of the microprocessorportion 36 is coupled to the input of the microprocessor portion 34. The"yes" output of the microprocessor portion 36 is coupled to a "promptoperator that oven setpoints are met" microprocessor portion 37.

The operator then presses a shelf key as represented by "shelf keypressed" microprocessor portion 38 in FIG. 3 which is, for example, thesecond pressing of the originally pressed product key. A microprocessorportion "has shelf key been selected already?" has a "no" output coupledto the input of the microprocessor portion 38. The microprocessorportion 39 has a "yes" output coupled to a "display shelfidentification" microprocessor portion 40. The output of the "displayshelf identification" microprocessor portion 40 is coupled to a "startcountdown timer n=1" microprocessor portion 41 which is coupled to an"is countdown timer finished" microprocessor portion 42. The "no" outputof the microprocessor portion 42 is coupled to the input of themicroprocessor portion 42 and the "yes" output of the microprocessorportion 42 is coupled to an "increment n" microprocessor portion 43.

The microprocessor portion 43 is coupled to a "load all parameters(t_(n), T_(n), H_(n), V_(n), R_(n)) into appropriate algorithm"microprocessor portions which are individually represented in FIG. 5 as"countdown timer" microprocessor portion 70 and in FIG. 4 as"temperature control algorithm" microprocessor portion 50, "humiditycontrol algorithm" microprocessor portion 51, "volumetric controlalgorithm" microprocessor portion 52, and "flow of circulation controlalgorithm" microprocessor portion 53.

The microprocessor portion 44 is coupled to an "enable all algorithmst_(n), T_(n), H_(n), V_(n), R_(n) " microprocessor portion 45 wheret_(n) at this portion represents all timers after timer t₁.

The microprocessor portion 45 is coupled to a "has t_(n) countdown timerfinished?" microprocessor portion 46. The "no" output of themicroprocessor portion 46 is coupled to the input of the microprocessorportion 45. The "yes" output of the microprocessor portion 46 is coupledto an "has last countdown timer t_(n) finished countdown?"microprocessor portion 47. The "no" output of the microprocessor portion47 is coupled to the input of the "8increment n" microprocessor portion43. The "yes" output of the microprocessor portion 47 is coupled to a"prompt operator that cook cycle is complete" microprocessor portion 48.

Referring now more particularly to FIG. 4 of the drawings, thetemperature control algorithm, for example, may be a complex algorithmhaving different temperatures at different time intervals or may be arelatively simple control algorithm having a constant temperature overthe heating or cooking period. In the event that the temperature controlalgorithm can be represented by a constant temperature over apredetermined time interval for a first product upon depression of afirst product key, and in the event that upon depression of a secondproduct key a temperature control algorithm for a second product has thesame temperature for a predetermined shorter time interval, then afterthe first key has been pressed twice and the product has been selectedand the shelf has been selected, the second product key can be pressedtwice to indicate the shelf for a second product to be heated or cookedduring a portion of the same time interval as the first product.

An oven temperature sensor circuit 15 and a temperature setpointregister 55 are coupled to the input of the "temperature controlalgorithm" microprocessor portion 50 for effecting a heat controlthrough a suitable heat control portion 56, which may, for example, be aclosed loop electric heat control. The temperature control algorithmwill be explained more fully subsequently.

In a similar manner humidity monitor 57 and a humidity setpoint register58 are coupled to a "humidity control algorithm" microprocessor portion51 for effecting humidity control as represented by a suitable humiditycontrol portion 59. This may be accomplished, for example, through aclosed loop steam injection control.

A flow rate monitor 60 and a flow rate setpoint register 61 are coupledto a "volumetric control algorithm" microprocessor portion 52 foreffecting volumetric flow rate control as represented by portion 60.This may be accomplished, for example, by closed loop adjustment of afan motor speed or closed loop adjustment of a duct aperture or closedloop adjustment of the axial position of a fan or a plurality of fans.Also, the axial position of a fan may be empirically determined forcontrol by a servomotor.

The closed loop adjustment of the fan motor speed may, for example,utilize a hot air duct and a flutter plate having an angular positiondetermined by the volumetric flow and controlling the rotary position ofa potentiometer which controls a variable-speed motor control for thefan.

A flow circulation setpoint register 62 is coupled to a flow circulationcontrol algorithm microprocessor portion 53 for effecting aircirculation control represented by block 63. This may be effected by anytechnique known to those skilled in the art. for example, by reversingthe rotational direction of a constant-speed or variable-speed axialflow fan in order to change the pattern of air flow within the oven.This fan may be the same fan as utilized in the humidity control portion59 and the volumetric flow rate control portion 60.

Referring now more particularly to FIG. 5 of the drawings, a typical"countdown timer" microprocessor portion 70 is represented. A "timersetpoint temperature" microprocessor portion 71 feds a setpointtemperature to the timer. An oven temperature sensor circuit 15 feedsthe actual oven temperature to the timer. A "linear orparameter-dependent time" microprocessor portion 73 also applies aninput to the timer. When the timer has counted down to zero, themicroprocessor portion 70 actuates a "timer done" portion 74.

Referring now more particularly to FIG. 6 of the drawings there isrepresented a cooking curve, for example, for baking a suitable foodproduct such as bread rolls. This cooking curve may be empiricallydetermined for each cooking product. The empirical data is representedin a look-up table with 100 being equal to real time or no adjustment.With reference to FIG. 7, an "enter setpoint temperature and cookingtime interval t_(n) " microprocessor portion 80 is coupled to a "cookingtime interval t_(n) " register 81 and to a "setpoint temperature"register 82. The register 81 is coupled to a clock 87 to set the clockfor countdown. The output of the "setpoint temperature" register 82 iscoupled to a "cooking curve look-up table" microprocessor portion 83which may contain the data represented by the graph of FIG. 6. The "oventemperature sensor circuit" 15 is also coupled to the microprocessorportion 83. A "cooking curve counter" microprocessor portion 85 isloaded with a value from the curve look-up table 83. The value in thelook-up table is determined by measuring the difference between theactual oven temperature and the setpoint temperature (desired cookingtemperature). If the actual temperature is below the setpointtemperature, the negative difference means a longer time then the realtime interval t_(n) is required for cooking to reach the setpointtemperature. The microprocessor includes an interrupt timer 86 whichtrips 100 times per second, for example. The interrupt timer decrementsthe cooking curve counter 85, for example, 100 times per second and thuswith the actual temperature equal to the setpoint temperature, thecooking curve counter will reach zero once every second. When the curvecounter reaches zero it decrements one second off the clock 87 which istiming the product. Thus the cooking time is parameter- dependent, forexample, temperature-dependent.

Referring to FIGS. 5 and 7, the "linear or parameter-dependent time"microprocessor portion 73 and the "countdown timer" microprocessorportion 70 preferably include, for example, the "cooking curve look-uptable" microprocessor portion 83, the "cooking curve counter"microprocessor portion 85, the "interrupt timer" microprocessor portion86, and the clock 87.

Referring now more particularly to FIG. 8 of the drawings, a motor 90rotates an air-movement device 91 which could, for example, be asquirrel cage fan. Steam may, for example, be injected by asolenoid-controlled injector 92 under the control of solenoid 93 andmoved by the fan 91. A humidity sensor 94 senses the humidity in theoven and applies a corresponding electrical signal to a comparator 95. Ahumidity setpoint register 96 applies an electrical signal representingthe desired humidity to a digital-to-analog converter 97 for applicationto the comparator 95. A pulsing circuit 98 having a pulsed output dutycycle proportional to the voltage input which represents the differencebetween the output signal of the humidity sensor 94 and the outputsignal of the digital-to-analog converter 97 controls the operation ofthe solenoid 93 which controls a suitable valve in the steam injector92.

Referring now more particularly to FIG. 9, a hot air duct 100 suppliesinside air or outside air or a combination of both as hot air toward aflutter plate 101 which rotates a potentiometer 102 in accordance withthe position of the flutter plate. The position of the flutter platedepends on the volumetric flow rate of hot air against the flutter platedirected by a fan 91. The output signal of the potentiometer 102 isapplied to a comparator 103 and a volumetric flow rate setpoint register104 applies a digital signal representing the desired flow rate to adigital-to-analog converter 1-5 which applies its output signal to thecomparator 103. The output signal of the comparator 103 representing thedifference between the signals from the potentiometer 102 and theconverter 105 is applied to a D.C. motor 106 to control the amount anddirection of rotation thereof. A lead screw 107 is coupled to the shaftof the D.C. motor 106 for positioning the baffle gate 108 to open orclose the hot air duct 111 in accordance with the setpoint of volumetricflow rate setpoint register.

Referring now more particularly to FIG. 10, another volumetric flow ratecontrol is represented. A hot air duct 114 supplies hot air toward oraway from a flutter plate 118 depending on the direction of rotation ofa squirrel cage fan 91 which is axially displaceable into and away fromthe hot air duct 114. The position of the flutter plate 118 depends onthe volumetric flow rate of hot air against the flutter plate directedby the fan 91. The fan 91 can be withdrawn from the duct with the effectthat as the fan is withdrawn less of the fan is in the hot air path andthe volumetric flow rate becomes smaller. The fan shaft 112 isconcentric with a motor shaft 113. A locking device, for example, aspline (not shown) allows the motor shaft 113 to turn the fan shaft 112while allowing the fan to be withdrawn from the duct. The fan motor 106preferably turns the fan at a constant speed. As the fan rotates, thefan may be withdrawn from or inserted into the duct by means of a slidelever 117 moved back and forth by an actuator motor 119 having a leadscrew 120. The actuating motor 119 can rotate clockwise andcounter-clockwise.

In a closed loop system, the volumetric flow positions a flutter plate118 which rotates a potentiometer 102 to convert the angular position ofthe flutter plate into a voltage. The voltage is applied to a comparator103. A digital volumetric flow rate parameter value is applied from aloaded volumetric flow rate setpoint register 104 to adigitial-to-analog converter 105 which is also coupled to the comparator103. If the two input voltages to the comparator are not the same, theoutput of the comparator will be positive or negative as determined bythe input voltages. The actuator motor 119 is driven by the outputsignal of the comparator 103 and moves counter-clockwise or clockwise,either to widthdraw the fan or insert the fan in the duct. The flutterplate in turn rises as the fan is inserted due to the greater volumetricflow or falls as the fan is withdrawn until the two input voltages tothe comparator are equal. This occurs for only one position of theflutter plate for a given volumetric flow rate value from the setpointregister 104 and digital-analog converter 105. Thus the flow rate can beset to any programmed input loaded into the register 104.

Occasionally products that are being baked have a consistency which issensitive to high velocity air flow, i.e., as the product rises, itsform is not yet solid. A high velocity fan will blow the product,causing an asymmetric and unpleasing aesthetic appearance. One way ofcontrolling the aesthetic appearance is by setting the volumetric flowrate at a sufficiently low value not to disturb the product. Twoexamples of the adjustment of the volumetric flow rate have beendescribed in connection with FIGS. 9 and 10.

Another way to control the aesthetic appearance and prevent skewing ofthe form of the product is to alternate the hot air flow circulation.This can be done by alternately changing direction of rotation of thefan.

The heating system may also be structured to include programmedmicroprocessor portions such that upon at least one of a plurality ofactuations of the first product selection key, the heating systemselects at least one parameter, for example, temperature, for a batch ofa given product and so that upon another actuation of the first productselection key indicates an oven location for the batch of the givenproduct. Thus, the product selection key may be actuated, for example,three times, and the first two actuations select the same temperaturefor two batches of a given product placed at different locations. Then,for example, the third actuation of the product selection key causes theheating system to indicate the oven locations for the batches of thegiven product.

While there have been described what are at present considered to be thepreferred embodiments of this invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the invention, and it is, therefore,aimed to cover all such changes and modifications as fall within thetrue spirit and scope of the invention.

What is claimed is:
 1. A parameter control system for controllingtemperature and volumetric flow rate for an oven for heating a foodproduct comprising:means for heating a heating medium in the oven; firstdigitally programmed means, having temperature sensing means and havingproduct keys and, having a predetermined temperature control algorithmcommunicating with said temperature sensing means and having programparameter variables per product key programmable for temperature valuesT₁, T₂, . . . T_(n) at time intervals t₁, t₂, . . .t_(n), respectively,where n equals 1, 2 . . . n to the number of intervals, and saiddigitally programmed means including closed loop heat control meanscontrolled by said algorithm, for controlling as a first parameter thetemperature of the heating medium; second digitally programmed means,having a predetermined volumetric control algorithm having programparameter variables per product key programmable for volumetric flowrate values V₁, V₂ . . . V_(n) at time intervals t₁, t₂ . . . t_(n),respectively, where n equals 1, 2 . . . n to the number of intervals,for controlling as a second parameter the volumetric flow rate of theheating medium; and said first digitally programmed means includingdigitally programmed means for controlling a plurality of time intervalsfor predetermined values of the temperature and for predetermined valuesof the volumetric flow rate, per product key, of the heating medium inthe oven.
 2. A system in accordance with claim 1 which includesprogrammed means for controlling as a third parameter the humidity ofthe heating medium and in which said means for controlling one or moretime intervals includes programmed means for controlling one or moretime intervals for a predetermined value of the humidity of the heatingmedium in the oven.
 3. A system in accordance with claim 1 in which aproduct key selects the programmed values of each of said parameters atpredetermined time intervals.
 4. A system in accordance with claim 2 inwhich a product key selects the programmed values of each of saidparameters at predetermined time intervals.
 5. A system in accordancewith claim 3 in which any of said time intervals is dependent on themeasured value of at least one of said parameters.
 6. A system inaccordance with claim 4 in which any of said time intervals is dependenton the measured value of at least one of said parameters.
 7. A system inaccordance with claim 3 in which said product key is ineffective toinitiate a cooking cycle unless one or more of said parameters is withinone or more predetermined tolerance bands around one or more givensetpoints.
 8. A system in accordance with claim 4 in which said productkey is ineffective to initiate a cooking cycle unless one or more ofsaid parameters is within one or more predetermined tolerance bandsaround one or more given setpoints.
 9. A system in accordance with claim1 in which said means for controlling said volumetric flow ratecomprises a fan and at least one of means for adjusting the rotary speedof said fan, means for adjusting the location of the fan and means foradjusting an aperture for the flow of the heating medium.
 10. A systemin accordance with claim 2 in which said means for controlling saidvolumetric flow rate comprises a fan and at least one of means foradjusting the rotary speed of the fan and means for adjusting anaperture for the flow of the heating medium.
 11. A parameter controlsystem for controlling temperature and humidity for an oven for heatinga food product comprising:means for heating a heating medium in theoven; first digitally programmed means, having temperature sensing meansand having product keys and, having a predetermined temperature controlalgorithm communicating with said temperature sensing means and havingprogram parameter variables per product key programmable for temperaturevalues T₁, T₂, . . . T_(n) at time intervals t₁, t₂, . . .t_(n),respectively, where n equals 1, 2 . . . n to the number of intervals,and said digitally programmed means including closed loop heat controlmeans responsive to said algorithm, for controlling as a first parameterthe temperature of the heating medium; second digitally programmedmeans, having a predetermined humidity algorithm having programparameter variables per product key programmable for humidity values H₁,H₂ . . . H_(n) at time intervals t₁, t₂ . . . t_(n), respectively, wheren equals 1, 2 . . . n to the number of intervals, including closed loophumidity control means and humidity monitoring means, for controlling asa second parameter the humidity of the heating medium; and said firstdigitally programmed means including digitally programmed means forcontrolling a plurality of time intervals for predetermined values ofthe temperature and predetermined values of the humidity, per productkey, of the heating medium in the oven.
 12. A parameter control systemfor controlling temperature and volumetric flow rate and humidity for anoven for heating a food product comprising:means for heating a heatingmedium in the oven; first digitally programmed means, having temperaturesensing means and having product keys and, having a predeterminedtemperature control algorithm communicating with said temperaturesensing means and having program parameter variables per product keyprogrammable for temperature values T₁, T₂, . . . T_(n) at timeintervals t₁, t₂, . . .t_(n), respectively, where n equals 1, 2 . . . nto the number of intervals, and said digitally programmed meansincluding closed loop heat control means responsive to said algorithm,for controlling as a first parameter the temperature of the heatingmedium; second digitally programmed means, having a predeterminedvolumetric control algorithm having program parameter variables perproduct key programmable for volumetric flow rate values V₁, V₂ . . .V_(n) at time intervals t₁, t₂ . . . t_(n), respectively, where n equals1, 2 . . . n to the number of intervals, including closed loopvolumetric flow rate control means and flow rate monitoring means, forcontrolling as a second parameter the volumetric flow rate of theheating medium; third digitally programmed means, having a predeterminedhumidity control algorithm having program parameter variables perproduct key programmable for humidity values H₁, H₂, . . . H_(n) at timeintervals t₁, t₂, t_(n), respectively, where n equals 1, 2 . . . n tothe number of intervals, including closed loop humidity control meansand humidity monitoring means, for controlling as a third parameter thehumidity of the heating medium; said first digitally programmed meansincluding digitally programmed means for controlling a plurality of timeintervals for predetermined values of the temperature and predeterminedvalues of the volumetric flow rate and predetermined values of thehumidity, per product key, of the heating medium in the oven.
 13. Asystem in accordance with claim 1 in which said second digitallyprogrammed means includes closed loop volumetric flow rate control meansand flow rate monitoring means.